As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of lamination layers of heat-seal plastic material, e.g. polyethylene films, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized in the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
To open the packages described above, various solutions have been proposed, including reclosable opening devices made of plastic material and substantially comprising a spout defining a through opening and fitted to a hole in a wall of the package, and a removable, e.g. screw or hinged, cap fitted to and outwardly closing the spout.
EP-A-2008787, discloses a method and apparatus for injection molding an opening device directly on a prelaminated hole, i.e. a hole formed in the base layer only and covered by the other lamination layers, including the layer of gas-barrier material, of the packaging material.
In practice, the molten plastic material is injected onto one side of the prelaminated hole to cover it up to an annular peripheral portion thereof and to form, in this way, a plastic material confetti portion directly attached to the prelaminated hole; the molten plastic material is then forced to pierce the prelaminated hole at such annular peripheral portion to form a pouring spout of the opening device projecting from an opposite side of the prelaminated hole and attached to the confetti portion through a smaller-section annular membrane connection portion adapted to be torn by the user to open the package.
In this way, the material forming the prelaminated hole is first pierced through and then resealed by the plastic material forming the spout. Therefore, the resulting package has gas-barrier properties.